1. Field of the Invention
The present invention relates to a polymer electrolyte, a rechargeable lithium battery including the polymer electrolyte, and a method of preparing the rechargeable lithium battery.
2. Description of the Related Art
The development of miniaturized portable electronics has created the need for a lighter and smaller rechargeable lithium battery with varying shapes.
Rechargeable lithium batteries can be classified into two categories, namely a lithium ion battery or a lithium ion polymer battery. The lithium ion polymer battery uses a solid electrolyte such as a polymer, unlike the lithium ion battery that uses a liquid electrolyte. The lithium ion polymer battery, therefore is lighter and has a smaller volume than the lithium ion battery. Furthermore, the lithium ion polymer battery is capable of being fabricated into various shapes.
Rechargeable lithium batteries with the polymer electrolyte can be further classified into a physical-gel battery and a chemical-gel battery.
The physical-gel battery may be manufactured in the following operations: an organic electrolyte solution is added to a polymer, the resulting mixture is heated to dissolve the polymer to create a paste, the paste is coated on a positive electrode and a negative electrode, the coated electrodes are assembled together with a separator to prepare an electrode element, the electrode element is inserted into a battery case, and the electrode element is then sealed within the battery case.
The polymer used in the physical-gel battery is usually a material that swells in an organic electrolyte solution at room temperature and dissolves at temperature ranges of 80 to 100° C. The swelling property affects gelation.
In the manufacturing process of the chemical-gel battery, a positive electrode, a separator, and a negative electrode are all assembled to produce an electrode element. The electrode element is then inserted into a battery case. An organic electrolyte, a vinyl monomer, and a polymerization initiator are injected into the battery case. Upon injection of the organic electrolyte, the vinyl monomer, and the polymerization initiator, the polymerization initiator reacts with the monomer to polymerize in the battery case, thereby fabricating the chemical-gel polymer battery.
The monomer used in the chemical-gel battery manufacturing process is one that readily swells in the organic electrolyte solution at room temperature.
The physical-gel battery and the chemical-gel battery have ionic conductivities in a range of about 2 mS/cm and about 3 mS/cm, respectively.
Both the physical-gel battery and the chemical-gel battery have drawbacks. The physical-gel battery has a drawback in that the polymer dissolves in the organic electrolyte solution when the temperature increases, and the resulting liquid leaks. One of the drawbacks of the chemical-gel battery includes the deterioration of charge due to incomplete polymerization between the vinyl monomer and the polymerization initiator. Another drawback of the chemical-gel battery is the reaction between the polymerization initiator and the vinyl monomer causing generation of gas. Yet another drawback of the chemical-gel battery is that the monomer is usually insufficiently polymerized to prepare a polymer electrolyte.